Under some conditions a flame can have an unstable discharge mode which, as a minimum, is undesirable for use of the flame and, in a worse circumstance, may burn out the apparatus. Even if such condition is a rarity it may be necessary or desirable to provide an automatic shutoff for the flame apparatus should the condition occur.
One type of flame generator susceptible to the problem is an inductively coupled plasma generator such as is used for quantitative spectral analysis. An example is disclosed in U.S. Pat. No. 4,766,287 (Morrisroe et al) of the present assignee and sold as a model P40 by The Perkin-Elmer Corporation, Norwalk, Conn.
Flame-out detectors are conventional, particularly for combustion flames such as in furnaces or torch devices. These detect light or heat from the flame and provide a feedback signal that typically turns off a fuel supply valve or pump motor. However, in certain circumstances an unstable flame, particularly in a plasma device, has an unstable mode that still emits light and heat. Therefore, flame-out detectors do not reliably protect against the circumstances of an instability.
Therefore objects of the present invention are to provide a novel detection apparatus for automatically extinguishing an unstable discharge of a flame, particularly for an inductively coupled plasma, and to provide an improved plasma apparatus capable of self-extinguishing the plasma in the event of an unstable plasma discharge.